Going back to the studies of women who consider themselves straight being more likely to have a same-sex experience, and women who consider themselves gay being more likely to have an opposite-sex experience, I can't help but wonder if it isn't at least partially due to cultural difference between the way we view the sexes.
I'm straight, and I've never kissed a woman, or anything like that, certainly not had sex with one. People often get confused, because, it seems, the cultural norm for females is to "experiment" in college or college years.
Since I was comfortable with my sexuality, I never felt any pressure to do so. However, I can imagine that some females who are more insecure would be pressured into having sexual experiences with people they are not attracted to, because women are "supposed to". We're supposed to be more fluid, we're supposed to have had a same-sex experience in college we can then tell our boyfriends about, and in some cultures, we're supposed to have sex with men even if we're gay.
So while it could be a very positive thing about females being more free to have experiences they want to have, and males being more frowned upon if they do, I think it could also be the opposite. There is definitely pressure for females to have sexual experiences with both genders, and to some extent much less trust that they're telling the truth when they say they're monosexual (not in the monogamous sense, in the gay or straight, not bi or pan sense).
So I think rather than basing it on experience, it would probably be more useful to ask people how much they are attracted to each gender, and possibly have a follow-up to see if it evolves during their lifetime.
It seems to me that it makes sense for someone to consider themselves straight or gay if they are, except for one person, for instance. It would seem dishonest to say "I'm bisexual" when the overwhelming majority of males or females does absolutely nothing for you. But I think that needs to be differentiated from being who do not have any attraction at all, but have had experiences, not because they wanted them, but because they felt they had to.